The present invention relates to automotive gearboxes and, more particularly, to a gearbox having an improved way of operably decoupling a countershaft assembly from the gearbox input shaft when the gearbox is placed in a direct drive mode.
My earlier U.S. Pat. No. 5,381,703 titled xe2x80x9cGearbox Countershaft Decouplerxe2x80x9d discloses an energy and performance saving alternative to conventional manual gearboxes by providing a way of operatively decoupling a countershaft assembly provided with change speed gears from the input shaft of the gearbox when the gearbox is operating in a direct drive mode. Because the countershaft assembly with its change speed gears is typically immersed in relatively viscus lubricant within the gearbox, a substantial amount of energy is consumed just in turning the countershaft and gears of the countershaft assembly. In my prior patent, therefore, when the gearbox is in the direct drive mode in which the input shaft is coupled directly to the output shaft without transferring power through the decoupled countershaft assembly, a substantial energy savings is obtained because the countershaft assembly does not turn. In the interest of completeness, my prior U.S. Pat. No. 5,381,703 is hereby incorporated by reference into the present specification.
While the decoupling arrangement of the ""703 patent has proven to be highly effective and successful in producing energy and performance savings, my prior arrangement has certain drawbacks with respect to space requirements and the need for additional shifting mechanisms. In this respect, it was found that original equipment gearbox housings could not be retrofitted with my prior mechanism because of an increased overall length of the mechanism. Furthermore, an additional shifting mechanism such as a fork, hydraulic clutch, or the like needed to be added to the overall mechanism, adding complexity and cost.
In accordance with my present invention, a manual transmission or gearbox that provides decoupling of the countershaft assembly in the direct drive mode can be retrofitted to existing transmissions and uses no extra room within the transmission casing or housing and requires no additional shift mechanisms. Furthermore, a transmission in accordance with the present invention does not lose any surface area contact between gears of the transmission and thus will not suffer in terms of strength and reliability over conventional arrangements. Additionally, the principles of the present invention can be applied to transmissions having many different change speed gears, can be utilized in synchromesh transmissions, and can also be utilized in connection with an auxiliary gearbox at the rear end of the drive train of a vehicle in association with a high/low speed gearbox.
In a preferred embodiment of the invention, the gearbox includes a shaft assembly comprising an input shaft and an output shaft in axial alignment with the input shaft. An input gear on the input shaft transfers driving power to a countershaft assembly in all modes other than the direct drive mode, and the countershaft assembly in turn drives an output gear that becomes drivingly coupled with the output shaft when a special two-part slider assembly on the shaft assembly, comprising a slider sleeve and a slider collar rotatably encircling the sleeve, is in a change speed position. On the other hand, when the slider assembly is in a direct drive position, the input gear is effectively decoupled from the input shaft and the slider assembly serves as the means by which driving power is transferred directly from the input shaft to the output shaft, completely bypassing the countershaft assembly and the output gear.
The input gear is hollow, presenting a recess or socket that faces the slider assembly and serves to telescopically receive the collar of the slider assembly. Thus, in the direct drive mode the collar is fully housed within the input gear and takes up no more of the axial length of the shaft assembly than the input gear itself. External teeth on the slider collar are in constant meshing engagement with internal teeth on the socket of the input gear, but internal teeth on the slider collar are received within an annular void on the input shaft when the slider assembly is in the direct drive position so as to avoid operative engagement between the slider collar and the input shaft at that time. Although this decouples the input gear from the input shaft, teeth on the sleeve part of the slider assembly mesh with a set of strategically located teeth on the input shaft at this time so that the slider sleeve receives driving input from the input shaft. That input power is then transferred directly by the slider sleeve to the output shaft through intermeshing teeth on the slider sleeve and the output shaft.
The slider sleeve is retained within the outer slider collar by releasable detent structure that also permits relative rotation between those two parts. Thus, they are releasably held together for conjoint movement along the shaft assembly when a shifter fork attached to the slider sleeve shifts the slider assembly between the direct drive position and a neutral position. However, the detent structure releases the slider sleeve when the fork shifts the sleeve to a further, change speed position in driving engagement with an output gear, leaving the slider collar behind in the input gear. The detent structure readily recouples the two parts of the slider assembly back together when the sleeve is pushed back into the collar to re-establish the neutral position or the direct drive position. Special yieldable stop structure on the input gear and the slider collar keeps the collar from being pulled completely out of the input gear when the slider sleeve is shifted into its change speed position from the neutral position.